In the case of an ink jet recording apparatus, ink is generally delivered to the recording head of the ink jet recording apparatus from an ink container through an ink delivery passage.
Because of the structure and/or the properties of the materials for an ink container and an ink delivery passage, it is unavoidable that air permeates through the walls of an ink container and/or ink delivery passage, and forms bubbles in the ink container and/or ink delivery passage. Further, it sometimes occurs that the changes in the ambient condition cause the air having dissolved into ink to form bubbles by separating from the ink. An ink container which does not have an ink absorbent member formed of a capillary substance, that is, an ink container which directly stores in its internal space, and the internal space of which is not in connection with the ambient air, is high in spatial efficiency, and also, can afford more latitude in ink selection, in terms of ink properties. However, if bubbles occur in an ink container of the abovementioned type, various problems occur.
For example, if it becomes impossible for an ink container of the above described type to maintain negative pressure because of the expansion of bubbles, ink leaks through the ink outlets of the recording head. Therefore, the internal space of an ink container of the abovementioned type has to be provided with a margin for bubble generation and bubble expansion. The provision of the margin increases an ink container in size. Further, if a bubble is trapped by a filter with which the ink delivery passage is provided, the ink delivery passage is virtually blocked by the trapped bubble, making it impossible for the ink delivery system to satisfactorily deliver ink. Therefore, the ink delivery passage and the filter therein have to be regularly subjected to a bubble extraction process. Moreover, if a bubble passes the filter and reaches the recording head, it prevents the recording apparatus from satisfactorily recording an image, or sometimes prevents the recording head from recording at all. If such a problem occurs, the bubbles in a recording head must be suctioned out or the recording head through the ink outlet.
Some ink jet recording apparatuses are provided with a subordinate ink container (which hereafter may be referred to as ink storage portion), in addition to an primary ink supply source (which hereafter may be referred to as main ink container, or simply as main container) which is not placed on a carriage. An ink storage portion is placed on a carriage and is connected to the recording head with the use of an ink delivery tube to supply the recording head with ink. If a bubble occurs in the subordinate ink container of an ink jet recording head of the above described type, it reduces the amount by which ink is delivered to the recording head. Thus, the subordinate ink container has to be regularly subjected to a process for extracting bubbles therefrom. In the case of the prior art for dealing with these problems described above, a subordinate ink container is made larger than necessary for storing a preset amount of ink, in order to tolerate the presence of a bubble.
In order to solve the above described problem, several proposals have been made regarding the method for removing a bubble from a subordinate ink container. According to one of the technologies in these proposals, for example, the bubbles in the ink delivery tube are made to float (separate from ink) and then, are suctioned out of the subordinate ink container, along with the ink in the ink delivery tube, by a pump (Japanese Laid-open Patent Application 2005-161770 (which corresponds to U.S. Patent Application No. 0088494/2005).
According to another of the technologies in the abovementioned proposals, it is determined with the use of an electrode whether or not the amount of the gas in the subordinate ink container is greater, than a preset value, and if the amount is greater than the preset value, the subordinate ink container is opened to the body of ambient air to force the gas out of the subordinate ink container by replenishing the subordinate ink container with ink (Japanese Laid-open Patent Application 2005-59491 (which corresponds to U.S. Patent Application No. 0109362/2007)
According to yet another of the technologies in the abovementioned-proposals, at the end of the process of replenishing a subordinate ink container with the ink from a primary ink supply source which is not on the carriage, the primary ink supply source is lowered to create a difference in head pressure, which is greater than the negative pressure in the subordinate ink container, so that a part of the body of ink in the subordinate ink container flows back, with bubbles, into the primary ink supply source until the amount of the negative pressure in the subordinate ink container falls to a value in a proper range (Japanese Laid-open Patent Application H10-244686 (which corresponds to U.S. Pat. No. 5,280,300, etc.).
Further, according to yet another of the technologies in the abovementioned proposals, a part of the tube for replenishing the subordinate ink container with ink is made of a substance capable of separating gas from the liquid in which the gas is contained, and the air in the body of ink in the tube is extracted by reducing the ambient pressure of the tube (Japanese Laid-open Patent Application 2003-159810 (which corresponds to J. S. Patent No. 6,742,877).
In the case of the technology disclosed in Japanese Laid-open Patent Application 2005-161770, which is for removing the bubbles in a subordinate ink container, it is unavoidable that the body of ink discharged with the bubbles when the bubbles are removed is wasted. In other words, this technology increases the operational cost of an ink jet recording apparatus. Further, this technology requires an absorbent member for absorbing and retaining the discharged ink, being therefore disadvantageous from the standpoint of reducing in size an ink jet recording apparatus. In the case of the technology disclosed in Japanese Laid-open Patent Application 2005-59491, a certain amount of space is necessary for measuring the amount of the gas with the use of an electrode, being therefore not suitable for reducing in size a subordinate ink container. In other words, this technology is not promising from the standpoint of spatial efficiency.
Further, the technology disclosed in Japanese Laid-open Patent Applications H10-244686, and 2005-161770 requires the primary ink supply source to be provided with a space for storing bubbles, in addition to the space for storing ink, making it necessary to increases in size the primary ink supply source. Thus, this technology is likely to increase an ink jet recording apparatus in size and cost. Moreover, in the case of the technology disclosed in Japanese Laid-open Patent Application 2003-159810, which employs a member for separating gas from the body of liquid into which the gas has dissolved, a bubble can be removed only when an ink jet recording apparatus is being driven, although ink is not wasted by the member for separating gas from the body of ink into which the gas has dissolved. Therefore, this technology is limited in terms of the condition under which a bubble can be removed.
As will be evident from the descriptions of the prior technologies given above, these technologies suffer from their own problems, but, are the same in that a bubble can be removed only when an ink jet recording apparatus is on. Therefore, if an ink jet recording apparatus is left for a long time without its power source turned on, as it is when an ink jet recording apparatus is kept in a storage, or left unused for a long time, the prior technologies are irrelevant.
Therefore, these technologies all tolerate the bubbles which generate in a subordinate ink container, and therefore, require a subordinate ink container to be larger in size than necessary for a preset amount of ink alone, making it difficult to realize a subordinate ink container which is significantly smaller in size than a subordinate ink container presently available. Further, increasing a subordinate ink container in storage size increases the subordinate ink container in the size of the interface between the body of ink therein, and the internal surface of the subordinate ink container. Therefore, the effect of the compatibility between the material for a subordinate ink container and the ink therein upon the performance of an ink jet recording apparatus (head) increases, limiting therefore the number of the substances selectable as the material for a subordinate ink container. Further, increasing a subordinate ink container in storage size is undesirable from the standpoint of the weight reduction of a subordinate ink container (it increases a subordinate ink container in weight).